Analyses of reproductive interactions that occur after heterospecific matings within the genus Caenorhabditis

Formation of zygotes in internally fertilizing organisms requires a number of successful interactions between oocytes and sperm within a receptive female reproductive tract. These interactions are usually assumed to be species-specific. For most species, it is either not possible to inseminate females with sperm from a different species or not possible to observe the consequences of such an insemination because the female is opaque. Nematodes of the genus Caenorhabditis are optically transparent and prior work indicates copulation between individuals of two different species is possible. We have used a series of vital stains and other cytological methods to analyze sperm after cross-species mating. We present here a series of analyses of the postcopulatory, prefertilization interactions among three Caenorhabditis species and find that reproductive biology is conserved, to varying degrees, among all three species. This approach allows investigation into which in vivo interactions between sperm and both oocytes and the somatic gonad have been maintained during the reproductive isolation that accompanies speciation.